Plate type heat exchanger



April 24-, 1951 H. H. EHRMAN PLATE TYPE HEAT EXCHANGER Filed Aug. 5,1948 w n m w m .h 4 H4 .1... r w. a m I M w w M. m m M Patented Apr. 24,1951 PLATE TYPE HEAT EXCHANGER Herbert H. Ehrman, York, Pa., assignor toYork Corporation, York, Pa., a corporation of Delaware ApplicationAugust 3, 1948, Serial No. 42,163

7 Claims.

This invention relate to heat exchangers of the plate type andparticularly .to exchangers of this character in which the plates aresheet metal stampings of the general type disclosed in the patent toSeligman No. 1,992,097, granted February 19, 1935, underwhichrapplicants assignee is licensed.

It is characteristicof heat exchangers of the Seligman type thatdifierent liquids exchange heat through the plate and that the plate hasapproximately trapezoidal embossed ribs Which are transverse to thedirection of flow of the two heat exchanging liquids. liquids may beconcurrent or countercurrent but in any case it is characteristic ofthis type of plate that the liquid flows alternately faster and slowerin successive portions of its path, a characteristic which is adopted toimprove the heat exchange. In the preferred form of plate, thetrapezoidal ribs are all in relief on one side of the plate and areformed by striking up the sheet metal of the plate. Thus, there aresubstantially identical patterns on opposite sides of the plate but oneis in relief and the other in intaglio.

This type of heat exchanger is used extensively in pasteurizing milk. Insuch a pasteurizer there usually are three sections, a heating section,and a cooling section in which respectively the milk exchanges heat witha hot fluid and with a wholly distinct cold fluid; and a regeneratingsection in which raw milk entering the pasteurizer derives heat frommilk leaving the holder. It is inevitable, in an arrangement of thissort, that the pressure heads on the various liquids will varythroughout each section. It results that certain of the plates aresubject to quite high pressure differentials.

Commercial embodiments of the Seligman invention make use of so-calledpips to positively space the plates. As shown at I8 and I9 in Fig. 7 ofthe patent to Groat No. 2,181,230, November 28, 1939, these are bossesstruck up from the plate and located in the wider intervals between thetwo plates, a location which is convenient for manufacturing reasons.

Experience with plates so designed demonstrates that the calculated heatexchange rates are sometimes not attained and that the losses ofpressure head of the various liquids in flow through the exchanger aresometimes greater than theoretically they should be. I have determinedthe fact that the plates can be, and actually are, materially displacedby the pressure differentials above mentioned, with the result that someof the more constricted parts of the The flows of the two flow pathbecome greatly restricted and throttle the flows materially.

One feature of the present invention involves the elimination of thepips from the wide interplate intervals and the location of spacing ribsdirectly in the restricted sections of the flow path. In this way thoseparts of the plate which define the most constricted, and therefore thecritical parts of the flow path, are positively spaced. This results ina, much smaller possible percentage change in the cross sectional areaof the constricted parts of the flow path. Indeed, as will be morereadily understood after a detailed description of the structure, anerror in the spacing produced by pips in the wide interplate intervalspermits and may even cause a greatly magnified error of spacing of theplates where the flow path is constricted.

Another source of loss in the operation of these plates is the fact thatthe cross ribs must terminate short of the side edges of the plate whichseal with one another, and this leaves a bypassage around the end ofeach cross rib. According to the present invention, the plates aredesigned to coordinate the cross sectional area of these by-passageswith the cross sectional area of the main flow path in such a way thatthe flow preference is toward the main path and away from theby-passages.

In attaining the above results, advantage is taken of thecharacteristics of an embossed sheet metal plate, and the desiredresults are secured without requiring the use of unusual or difficultmanufacturing methods.

The invention will now be described by reference to the accompanyingdrawing in which: a

Fig. 1 is a face view of the upper end of a right-hand plate andincludes the first, second and third ribs.

Fig. 2 is a section of assembled plates on the line 2-2 of Fig. 1.Counting from the top this view shows a right-hand, left-hand,right-hand and left-hand plate assembled, and is drawn at a larger scalethan that of Fig. 1. The middle portion is broken away to reduce thehorizontal extent of the view.

Fig. 3 is a fragmentary section (at a still larger scale) taken on theline 3-3 of Fig. 1.

Fig. 4 is a fragmentary section on the line 4-4 of Fig. 1 and at thesame scale as Fig. 3.

Fig. 5 is a fragmentary section on the line 55 of Fig. 1. The scale islarger than that of Fig. 1.

Fig. 6 is a fragmentary section on the line 6-6 of Fig. 1.

Fig. 7 is a fragmentary section on the line of Fig. 1.

With reference to the designations righthand and left-hand, it will behelpful to explain that in any group of assembled plates, two liquidsare handled and each liquid must flow through alternate inter-plateintervals. Thus, at each of the four corners there is a port. Two ofthese (generally diagonally opposed) communicate with the face intervaland the other two with the back interval, but such communication isthrough face ports in the next plate to the rear. Consequentlysuccessive plates as assembled must have passages leading from alternatecorner ports to their respective front faces. To distinguish them, theplates are arbitrarily called rights and lefts. The plates are otherwiseidentical except for reversed arrangement of spacing lugs hereinafterexplained.

The right-hand plate shown in Fig. 1 is generally indicated by thenumeral TR and in other figures right-hand plates are designatedgenerally by TR; and left-hand plates by EL. Again referring to Fig. l,the slot which engages the support bar is shown at 8, it beingunderstood that the plates when separated hang in vertical positionsfrom a bar. All the plates are slidable along the bar and when in useare clamped be tween adjustable end plates to which the liquid conduitsare connected. When the plates are so 1 (see Figs. 2 and 3) and hascross-corner portions 12, and ring portions M the latter of whichsurround the corner port IS. The portions E2 and Hi are continuous sothat the face of the plate is isolated from port it.

To seal with the gasket of the next plate to the rear (a left-handplate) and afford fiow passages on the face side of the plate, that partof port I! not surrounded by the gasket [2 is surrounded by rearwardlyembossed portions iii of the plate separated by bridges 15. Similarrearwardly embossed portions I8 separated by bridges E9 overlie thecross-corner portion of the gasket on the'next plate to the rear. Fig. 7shows how the metal is folded together and welded to form the bridgesl9. Bridges are formed in the same way.

Whil Fig. 1 shows only the upper two ports 16 and H, it will be obviousto those skilled in the art that companion ports diagonally opposed toports l5 and 11 are located at the lower end of the plate (see Fig. 3 ofSeligman 1,992,097 or Fig. 1 of Seligman et al. 2,075,236) and that portconnections to the face of the plate are reversed as between right-handand left-hand plates.

All the details so far described except the welded bridges l5 and 19 areknown in the-art and have been embodied in commercial exchangers byapplicant's assignee.

Extending across the plate from gasket to gasket are corrugationsforming ribs 2i, the upper three of which appear in Fig. 1. These ribs,as viewed in cross section in Fig. 4, are isosceles trapezoids. and formanufacturing convenience they are all raised in the same direction'fromthe plane ofthe plate proper. For convenience in description the part 22will be called the top of the rib, the portions 23 the inclined sides ofthe rib, and the portion 24 between ribs the base. Short-radius filletsare used, as shown.

Just as is the case in Seligrnan 1,992,097 (see Fig. 6 of the patent)the efiect of assembling plates in a stack is to produce restrictedVenturi throats V interposed between enlarged spaces E. According to thepresent invention positive spac ing of the plates is assured by bosseswhich engage in the throat V and serve to inhibit undesired overconstriction of these throats.

The preferred construction is to form on the inclined sides of the ribscylindrical bosses arranged in pairs in which one boss 25R is struckinward and the other 26B is struck outward.

Three such pairs are shown in Fig. 1 which shows.

a right-hand plate. On the left-hand plates the pairs are similarlylocated but as best shown in Fig. 2 bosses 25L are struck outward and26L inward. V

The efiect is to cause the bosses on one plate to engage bosses on thenext. This can best be understood by examining Fig. 5 and having dueregard for the plane of section. Bosses 25R on the first and thirdplates respectively engage bosses 25L on the second and fourth plates.There is no engagement visible in Fig. 5 between the second and thirdplates but as will be clear from Fig. 2, bosses 26L on the second platedo engage bosses 26R on the third plate. Such en'- gagement occursthroughout the entire series of plates and (in the form illustrated) atthree spaced points in the length of every rib.

Each rib 2% ends in an inclined surface 27 leading from the inner marginof gasket 9' to the top 22 of the rib. As best shown in Fig. 3 theeiiectis to afi'ord a passage B past the end of the rib. This affordsuseful heat exchange surface provided the passage B isnot unduly wide,as it always has been heretofore. The degree of constriction is afunction of the steepness of the surface According to the invention, theflow resistance at B (Fig. 3) is made equal to or greater than (i. e.not" less than) the new resistance offered by two Venturi restrictions V(Fig. 4) operating'in series. The effect is to assure approximatelyuniform flow past all portions of the rib, so that all exchange surfaceoperates efilciently'. Since gasket sealing pressures and fluid pressured 'i'eiiti'al's tend tochange the width of passage 35' local means tomaintain it are provided by forming outward bosses 28 arid inward bosses29 along each corner at the" ends of the ribs 2! as best shown inFig's.3a'nd 6.

Quite obviously a small'er'ror in the spacing at the large inter plateintervals between" tops and between bases will have a minor efi'e'ct onthe throttling at E. Becauserestrictions V are smaller and because ofthe inclined relation, an error in spacing" at E" will produce" agreatly magnified percentage error in spacing'at'V, and it is thisfac'tthatled to the location of the'bosses 25; 25' so" as to" rigidlyspace the plates at the restricted throats V The invention can beapplied to plates of various different'des-igns. The efiec't is to spacethe plates accurately at the constrictions, where accurate spacing isimportant. Having thus stabilized flow conditions itthen becomespracticable tdedua'li'ze flow conditions as between all parts of everyrib. The bridges I 5 and I9 perform a like effect by sustaining clampingand hydrostatic pressures at the pbints'iridicatedwherc the plates havelarge fiat areas not adequately spaced in' the constructions used in theprior art.

What'is claimed is:'

1. In a heat exchanger of the't'ypeiinwhich a plurality of platesiiispaced fa'ce'to rabe" relation seal at their margins and" are portedto" provide for the flow of diverse fluids between plates and thus alongthe opposite faces of individual plates, the improvement which consistsin forming the plates with corrugations transverse to the flow of saidfluids, said corrugations being approximately isosceles trapezoids incross section and so arranged as to afford substantially identicalpatterns on opposite faces of the plate, each pattern being relief wherethe other pattern is in intaglio, said corrugations throughout the heatexchange area of the plate having on their inclined lateral faces seriesof spaced bosses which engage inclined portions of opposed corrugationson at least one proximate plate, the bosses of respective series onsuccessive plates being olfset relatively to those on adjacent plates inthe directions of the lengths of the corrugations, said series of bossesserving to space adjacent plates positively substantially throughout theareas within said margins, and at points where the interplate intervalis relatively small.

2. The improvement defined in claim 1 in which the entire rib design inone face of the various plates is in relief and that on the oppositeface is in intaglio.

3. The improvement defined in claim 1 in which the entire rib design inone face of the various plates is in relief and that on the oppositeface is in intaglio, and the bosses are arranged in pairs, in each ofwhich pairs one boss is struck outward and the other inward.

4. The improvement defined in claim 1 in which the entire rib design inone face of the various plates is in relief and that on the oppositeface is in intaglio, the bosses are arranged in pairs in each of whichpairs one boss is struck outward and the other inward, and the bosses ofeach pair are interchanged as to position on alternate plates in thegroup.

5. The improvement defined in claim 1 in which the corrugations formribs which terminate adjacent the sealing margins of the plate insurfaces so steeply inclined to the general plane of the plate thatbetween adjacent rib ends on two assembled plates, the flow interval issulficiently restricted to offer resistance to flow at least as great asthat offered to flow over the rib.

6. The improvement defined in claim 1 in which the corrugations formribs which terminate adjacent the sealing margins of the plate in endsurfaces which are steeply inclined to the general plane of the plate,and pairs of oppositely projecting bosses are formed on the folds wherethe end surfaces meet the side surfaces of the ribs and aifordinter-plate engagemenh which maintains spacing of the end surfaces ofassembled plates.

7. In a heat exchanger of the type in which a plurality of plates spacedin face to face relation seal at their margins and are ported to providefor the flow of diverse fluids between plates and thus along theopposite faces of individual plates, the improvements which consist informing a part of the plate adjacent the ports without corrugations andanother part of the plate more remote from the ports with corrugationstransverse to the flow of said fluids said corrugations beingapproximately isosceles trapezoids in cross section and so arranged asto afford substantially identical patterns on opposite faces of theplate each pattern being in relief where the other pattern is inintaglio, said corrugations throughout the heat exchange area of theplate, having on their inclined lateral faces series of spaced bosseswhich engage inclined portions of opposed corrugations on at least oneproximate plate, the bosses of respective series on successive platesbeing offset relatively to those on adjacent plates in the directions ofthe lengths of the corrugations, said series of bosses serving to spaceadjacent plates positively substantially throughout the areas withinsaid margins, and at points where the interplate interval is relativelysmall; the parts of the plates devoid of corrugations being embossed todefine flow channels on one face of the plate and sealing ribs on theother face thereof, said channels being divided by cross bridges whichstiffen said sealing ribs and are each formed by folding a pleat in themetal of the plate in a direction transverse to the rib, said pleatbeing welded on the rib-forming side of the plate so as to maintain thecontinuity of the rib.

HERBERT H. EHRMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,039,216 Feldmeir Apr. 28, 19362,181,230 Groat Nov. 28, 1939 FOREIGN PATENTS Number Country Date561,314 Great Britain Jan. 18, 1943 64,868 Denmark Sept. 30, 1946

